Freeze-drying for controlled nanoparticle distribution in Co/SiO2 Fischer–Tropsch catalysts

• Published in: Journal of catalysis 2013-01, Vol.297, p.306-313
• Main Authors: Eggenhuisen, T.M., Munnik, P., Talsma, H., de Jongh, P.E., de Jong, K.P.
• Format: Article
• Language: English
• Subjects: Calorimetry; Catalysis; Catalyst preparation; catalysts; Chemistry; Cobalt; Colloidal state and disperse state; Deactivation; Dehydration; differential scanning calorimetry; drying; Exact sciences and technology; Fischer–Tropsch synthesis; Freeze drying; Freezing; General and physical chemistry; Lyophilization; melting; Nanoparticle synthesis; Nanoparticles; nitrates; nitrogen; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Silica; silica gel; Sintering; Supported catalysts; temperature; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Transition metal nitrates
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2012.10.024

Freeze-drying was successfully applied to control the nanoparticle distribution in Co/SiO2 Fischer–Tropsch catalysts with 4–8nm Co3O4 nanoparticles prepared from a cobalt nitrate precursor. As-synthesized catalysts with clusters, uniformly distributed nanoparticles or an egg-shell configuration on a silica-gel support form a platform to study the effect of nanoparticle spacing on deactivation by sintering. [Display omitted] ► Cobalt nanoparticle distribution on a commercial silica gel was manipulated. ► Freeze-drying parameters were established using differential scanning calorimetry. ► Conventional drying led to 10–400nm clusters of 6–8nm Co3O4 nanoparticles. ► Uniformly distributed 4–7nm nanoparticles were obtained by freeze-drying. ► Model systems synthesized for deactivation studies for the Fischer–Tropsch reaction. Controlling the nanoparticle distribution over a support is considered essential to arrive at more stable catalysts. By developing a novel freeze-drying method, the nanoparticle distribution was successfully manipulated for the preparation of Co/SiO2 Fischer–Tropsch catalysts using a commercial silica-gel support. After loading the precursor via a solution impregnation or melt infiltration, differential scanning calorimetry was used to study the phase behavior of the confined cobalt nitrate precursor phases to ascertain suitable freeze-drying conditions. When a conventional drying treatment was utilized, catalysts showed inhomogeneous cobalt distributions, with 6–8nm nanoparticles grouped in clusters of up to 400nm. In contrast, by utilizing freeze-drying starting at liquid nitrogen temperatures, homogeneous distributions of 4–7nm nanoparticles were obtained. Raising the temperature at which the freeze-drying process takes place resulted in either uniform or strongly non-uniform nanoparticle distributions, depending on the specific conditions and precursor loading method. After reduction, all catalysts showed high activity for the Fischer–Tropsch reaction at 1bar. The catalysts thus synthesized form an excellent platform for future studies of the stability under industrially relevant Fischer–Tropsch conditions.